Welcome to the SBO forum.
Sounds like the metals used on the boat had corrosion issues.
Your concern sounds well founded.
- Have you had the boat out of the water for inspection?
- Are there signs of corrosion on the post in the area of the quadrant?
- Was the boat submerged at some point?
- Is there unusual movement in the rudder?
- Does it have a gudgeon/pintle design?
- Is the base sound?
Your query drives a lot of questions that might help address your basic question. Can I trust the boat?
With older boats of that size you either need to do the inspection or have a skilled craftsman inspect the boat. Other's experiences can only lead to more suspicion and more questions.